1
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Targeting lipid biosynthesis pathways for hepatitis B virus cure. PLoS One 2022; 17:e0270273. [PMID: 35925919 PMCID: PMC9352027 DOI: 10.1371/journal.pone.0270273] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Accepted: 06/07/2022] [Indexed: 12/13/2022] Open
Abstract
Chronic hepatitis B virus (HBV) infection is characterized by the presence of high circulating levels of non-infectious lipoprotein-like HBV surface antigen (HBsAg) particles thought to contribute to chronic immune dysfunction in patients. Lipid and metabolomic analysis of humanized livers from immunodeficient chimeric mice (uPA/SCID) revealed that HBV infection dysregulates several lipid metabolic pathways. Small molecule inhibitors of lipid biosynthetic pathway enzymes acetyl-CoA carboxylase (ACC), fatty acid synthase, and subtilisin kexin isozyme-1/site-1 protease in HBV-infected HepG2-NTCP cells demonstrated potent and selective reduction of extracellular HBsAg. However, a liver-targeted ACC inhibitor did not show antiviral activity in HBV-infected liver chimeric mice, despite evidence of on-target engagement. Our study suggests that while HBsAg production may be dependent on hepatic de novo lipogenesis in vitro, this may be overcome by extrahepatic sources (such as lipolysis or diet) in vivo. Thus, a combination of agents targeting more than one lipid metabolic pathway may be necessary to reduce HBsAg levels in patients with chronic HBV infection.
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2
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El-Mokhtar MA, Hetta HF, Mekky MA, Abd El-Kareem DM, Ramadan M, Salah M, Mohamed NA, El-Masry EA, Adel S, Sayed IM. Characterization of Antigen Escape Mutations in Chronic HBV-Infected Patients in Upper Egypt. Infect Drug Resist 2021; 14:2419-2427. [PMID: 34234472 PMCID: PMC8254413 DOI: 10.2147/idr.s315299] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2021] [Accepted: 05/24/2021] [Indexed: 12/27/2022] Open
Abstract
Background Mutations within the “a” determinant region (position 124–147) that is present in the major hydrophilic region (MHR, position 99–160) of the hepatitis B surface antigen (HBsAg) are associated with vaccine-escape, lack of diagnosis, and failure to hepatitis B immunoglobulin (HBIG) therapy. Data regarding the amino acid changes of “a” determinant region of HBsAg are limited in Egypt. The prevalence and mutations in this region among chronic HBV (CHB)-infected patients in Upper Egypt are not known. Material and Methods Blood samples were collected from HBsAg-positive CHB-infected patients (n=123) admitted to Assiut University Hospitals. Serum samples were screened for HBsAg, HBeAg, anti-HBs and anti-HBe antibodies using commercially available ELISA kits. Viral load was determined by qPCR. In addition, mutational analysis was carried out targeting the HBV surface gene to determine the HBV genotype and vaccine escape mutations. Results Sequencing analysis of HBV DNA revealed that genotype D is the major circulating type (81.3%), followed by genotype E (18.7%). Analysis of the HBV genome revealed that 103/123 (83.7%) patients showed wild-type sequences and 20/123 (16.3%) showed mutations in the HBsAg gene. Mutation in seventeen patients (17/20, 85%) showed only one mutation, and three patients showed two mutations (3/20, 15%) in the “a” determinant region. The observed mutations were T115S (3/20, 15%), P120T/S (3/20, 15%), T126S (1/20, 5%), Q129R (2/20, 10%), M133T (2/20, 10%), S143L (5/20, 25%), D144E/A (3/20, 15%), and G145R/A (4/20, 20%). Mutations in the “a” determinant region were detected in genotype D isolates only. Conclusion We described for the first time the prevalence and characterization of vaccine escape mutants in CHB patients in Upper Egypt. Mutational analysis of the “a” determinant region revealed the presence of a wide spectrum of mutants in the circulating HBV isolates that could be a potential threat to HBV diagnosis, therapy success, and HBV vaccination program in Upper Egypt.
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Affiliation(s)
- Mohamed A El-Mokhtar
- Department of Medical Microbiology and Immunology, Faculty of Medicine, Assiut University, Assiut, 71515, Egypt
| | - Helal F Hetta
- Department of Medical Microbiology and Immunology, Faculty of Medicine, Assiut University, Assiut, 71515, Egypt
| | - Mohamed A Mekky
- Department of Tropical Medicine and Gastroenterology, Assiut University Hospital, Assiut, Egypt
| | - Doaa M Abd El-Kareem
- Department of Clinical Pathology, Faculty of Medicine Assiut University, Assiut, Egypt
| | - Mohammed Ramadan
- Microbiology and Immunology Department, Faculty of Pharmacy Al-Azhar University-Assiut branch, Assiut, 71526, Egypt
| | - Mohammed Salah
- Microbiology and Immunology Department, Faculty of Pharmacy Port Said University, Port Said, 42526, Egypt
| | - Nahed A Mohamed
- Department of Medical Biochemistry, Faculty of Medicine, Assiut University, Assiut, Egypt
| | - Eman A El-Masry
- Microbiology and Immunology Unit, Department of Pathology, College of Medicine, Jouf University, Al-Jouf, Saudi Arabia.,Department of Medical Microbiology and Immunology, College of Medicine, Menoufia University, Menoufia, Egypt
| | - Sara Adel
- Department of Clinical Pathology, Faculty of Medicine, Al-Azhar University, Assiut, 71515, Egypt
| | - Ibrahim M Sayed
- Department of Medical Microbiology and Immunology, Faculty of Medicine, Assiut University, Assiut, 71515, Egypt.,Department of Pathology, School of Medicine, University of California, San Diego, CA, 92093, USA
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3
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Vaillant A. HBsAg, Subviral Particles, and Their Clearance in Establishing a Functional Cure of Chronic Hepatitis B Virus Infection. ACS Infect Dis 2021; 7:1351-1368. [PMID: 33302622 DOI: 10.1021/acsinfecdis.0c00638] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
In diverse viral infections, the production of excess viral particles containing only viral glycoproteins (subviral particles or SVP) is commonly observed and is a commonly evolved mechanism for immune evasion. In hepatitis B virus (HBV) infection, spherical particles contain the hepatitis B surface antigen, outnumber infectious virus 10 000-100 000 to 1, and have diverse inhibitory effects on the innate and adaptive immune response, playing a major role in the chronic nature of HBV infection. The current goal of therapies in development for HBV infection is a clinical outcome called functional cure, which signals a persistent and effective immune control of the infection. Although removal of spherical SVP (and the HBsAg they carry) is an important milestone in achieving functional cure, this outcome is rarely achieved with current therapies due to distinct mechanisms for assembly, secretion, and persistence of SVP, which are poorly targeted by direct acting antivirals or immunotherapies. In this Review, the current understanding of the distinct mechanisms involved in the production and persistence of spherical SVP in chronic HBV infection and their immunoinhibitory activity will be reviewed as well as current therapies in development with the goal of clearing spherical SVP and achieving functional cure.
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Affiliation(s)
- Andrew Vaillant
- Replicor Inc., 6100 Royalmount Avenue, Montreal, Quebec H8Y 3E6, Canada
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4
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Hyrina A, Jones C, Chen D, Clarkson S, Cochran N, Feucht P, Hoffman G, Lindeman A, Russ C, Sigoillot F, Tsang T, Uehara K, Xie L, Ganem D, Holdorf M. A Genome-wide CRISPR Screen Identifies ZCCHC14 as a Host Factor Required for Hepatitis B Surface Antigen Production. Cell Rep 2020; 29:2970-2978.e6. [PMID: 31801065 DOI: 10.1016/j.celrep.2019.10.113] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2019] [Revised: 06/23/2019] [Accepted: 10/28/2019] [Indexed: 12/24/2022] Open
Abstract
A hallmark of chronic hepatitis B (CHB) virus infection is the presence of high circulating levels of non-infectious small lipid HBV surface antigen (HBsAg) vesicles. Although rare, sustained HBsAg loss is the idealized endpoint of any CHB therapy. A small molecule, RG7834, has been previously reported to inhibit HBsAg expression by targeting terminal nucleotidyltransferase proteins 4A and 4B (TENT4A and TENT4B). In this study, we describe a genome-wide CRISPR screen to identify other potential host factors required for HBsAg expression and to gain further insights into the mechanism of RG7834. We report more than 60 genes involved in regulating HBsAg and identify additional factors involved in RG7834 activity, including a zinc finger CCHC-type containing 14 (ZCCHC14) protein. We show that ZCCHC14, together with TENT4A/B, stabilizes HBsAg expression through HBV RNA tailing, providing a potential new therapeutic target to achieve functional cure in CHB patients.
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Affiliation(s)
- Anastasia Hyrina
- Novartis Institutes for BioMedical Research, Emeryville, CA 94608, USA.
| | - Christopher Jones
- Novartis Institutes for BioMedical Research, Emeryville, CA 94608, USA
| | - Darlene Chen
- Novartis Institutes for BioMedical Research, Emeryville, CA 94608, USA
| | - Scott Clarkson
- Novartis Institutes for BioMedical Research, Cambridge, MA 02139, USA
| | - Nadire Cochran
- Novartis Institutes for BioMedical Research, Cambridge, MA 02139, USA
| | - Paul Feucht
- Novartis Institutes for BioMedical Research, Emeryville, CA 94608, USA
| | - Gregory Hoffman
- Novartis Institutes for BioMedical Research, Cambridge, MA 02139, USA
| | - Alicia Lindeman
- Novartis Institutes for BioMedical Research, Cambridge, MA 02139, USA
| | - Carsten Russ
- Novartis Institutes for BioMedical Research, Cambridge, MA 02139, USA
| | | | - Tiffany Tsang
- Novartis Institutes for BioMedical Research, Emeryville, CA 94608, USA
| | - Kyoko Uehara
- Novartis Institutes for BioMedical Research, Emeryville, CA 94608, USA
| | - Lili Xie
- Novartis Institutes for BioMedical Research, Emeryville, CA 94608, USA
| | - Don Ganem
- Novartis Institutes for BioMedical Research, Emeryville, CA 94608, USA
| | - Meghan Holdorf
- Novartis Institutes for BioMedical Research, Emeryville, CA 94608, USA
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5
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Seitz S, Habjanič J, Schütz AK, Bartenschlager R. The Hepatitis B Virus Envelope Proteins: Molecular Gymnastics Throughout the Viral Life Cycle. Annu Rev Virol 2020; 7:263-288. [PMID: 32600157 DOI: 10.1146/annurev-virology-092818-015508] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
New hepatitis B virions released from infected hepatocytes are the result of an intricate maturation process that starts with the formation of the nucleocapsid providing a confined space where the viral DNA genome is synthesized via reverse transcription. Virion assembly is finalized by the enclosure of the icosahedral nucleocapsid within a heterogeneous envelope. The latter contains integral membrane proteins of three sizes, collectively known as hepatitis B surface antigen, and adopts multiple conformations in the course of the viral life cycle. The nucleocapsid conformation depends on the reverse transcription status of the genome, which in turn controls nucleocapsid interaction with the envelope proteins for virus exit. In addition, after secretion the virions undergo a distinct maturation step during which a topological switch of the large envelope protein confers infectivity. Here we review molecular determinants for envelopment and models that postulate molecular signals encoded in the capsid scaffold conducive or adverse to the recruitment of envelope proteins.
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Affiliation(s)
- Stefan Seitz
- Department of Infectious Diseases, University of Heidelberg, 69120 Heidelberg, Germany;
| | - Jelena Habjanič
- Bavarian NMR Center, Department of Chemistry, Technical University of Munich, 85748 Garching, Germany.,Institute of Structural Biology, Helmholtz Zentrum München, 85764 Neuherberg, Germany
| | - Anne K Schütz
- Bavarian NMR Center, Department of Chemistry, Technical University of Munich, 85748 Garching, Germany.,Institute of Structural Biology, Helmholtz Zentrum München, 85764 Neuherberg, Germany
| | - Ralf Bartenschlager
- Department of Infectious Diseases, University of Heidelberg, 69120 Heidelberg, Germany; .,Division of Virus-Associated Carcinogenesis, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
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6
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Cavallone D, Ricco G, Oliveri F, Colombatto P, Moriconi F, Coco B, Romagnoli V, Salvati A, Surace L, Bonino F, Brunetto MR. Do the circulating Pre-S/S quasispecies influence hepatitis B virus surface antigen levels in the HBeAg negative phase of HBV infection? Aliment Pharmacol Ther 2020; 51:1406-1416. [PMID: 32390175 DOI: 10.1111/apt.15753] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/25/2019] [Revised: 11/19/2019] [Accepted: 04/06/2020] [Indexed: 12/18/2022]
Abstract
BACKGROUND Virus, host factors and their interplay influence Hepatitis B surface Antigen serum levels during Hepatitis B Virus (HBV) infection course and treatment. AIM To study the Pre-S/S circulating quasispecies in a cohort of untreated, HBeAg negative, genotype-D, HBsAg carriers. METHODS We studied 260 carriers: 71 with HBeAg negative infection (ENI; HBV-DNA ≤2000 IU/mL); 42 Grey Zone (GZ; HBV-DNA ≤20 000 IU/mL); 82 chronic hepatitis (CH) and 65 cirrhosis (CI) (HBV-DNA > 20 000 IU/mL). Population sequencing was applied to identify Pre-S/S gene mutations responsible for any amino acid substitution or potential biological/antigenic implications (M-muts) on HBsAg. RESULTS HBsAg serum levels were lower in ENI + GZ than in CH + CI (2.61 [-1.10/4.06] vs 3.62 [2.41/4.92] log10 IU/mL, P < 0.001) and in CI than CH (3.48 [2.41/4.38] vs 3.66 [2.57/4.92] log10 IU/mL, P < 0.001). M-muts were found in 73 (28.1%) cases: 5 (7.0%) ENI, 3 (7.1%) GZ, 26 (31.7%) CH, 39 (60.0%) CI (P < 0.001) and mostly in Pre-S2 (17.6%) than Pre-S1 (5.8%) and Small-S (10.8%; P < 0.001). Overall HBsAg serum levels were higher in carriers with M-muts (3.56 [0.95/4.38] vs 3.17 [-1.10/4.92] log10 IU/mL, P < 0.001), but comparable in carriers with or without M-mut when considering separately ENI + GZ (2.84 [0.95/3.89] vs 2.61 [-1.10/4.06] log10 IU/mL, P = 0.330] and CH + CI (3.57 [2.67/4.38] vs 3.63 [2.41/4.92] log10 IU/mL, P = 0.37). Infection phase (β: 0.422, P < 0.001), age (β: -0.260, P < 0.001), ALT (β: -0.103, P = 0.045), liver stiffness (β: -0.118, P = 0.039) and HBV-DNA (β: 0.384, P < 0.001), but not M-mut were independently associated with HBsAg serum levels. CONCLUSIONS In HBeAg negative, genotype-D, carriers Pre-S/S heterogeneity increases with severity of liver disease, but does not influence HBsAg serum levels, that in low viraemic carriers are associated with an effective control of HBV.
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Affiliation(s)
- Daniela Cavallone
- Department of Clinical and Experimental Medicine, University of Pisa, Pisa, Italy.,Hepatology Unit and Laboratory of Molecular Genetics and Pathology of Hepatitis Viruses, Pisa University Hospital, Pisa, Italy
| | - Gabriele Ricco
- Department of Clinical and Experimental Medicine, University of Pisa, Pisa, Italy.,Hepatology Unit and Laboratory of Molecular Genetics and Pathology of Hepatitis Viruses, Pisa University Hospital, Pisa, Italy
| | - Filippo Oliveri
- Hepatology Unit and Laboratory of Molecular Genetics and Pathology of Hepatitis Viruses, Pisa University Hospital, Pisa, Italy
| | - Piero Colombatto
- Hepatology Unit and Laboratory of Molecular Genetics and Pathology of Hepatitis Viruses, Pisa University Hospital, Pisa, Italy
| | - Francesco Moriconi
- Hepatology Unit and Laboratory of Molecular Genetics and Pathology of Hepatitis Viruses, Pisa University Hospital, Pisa, Italy
| | - Barbara Coco
- Hepatology Unit and Laboratory of Molecular Genetics and Pathology of Hepatitis Viruses, Pisa University Hospital, Pisa, Italy
| | - Veronica Romagnoli
- Hepatology Unit and Laboratory of Molecular Genetics and Pathology of Hepatitis Viruses, Pisa University Hospital, Pisa, Italy
| | - Antonio Salvati
- Hepatology Unit and Laboratory of Molecular Genetics and Pathology of Hepatitis Viruses, Pisa University Hospital, Pisa, Italy
| | - Lidia Surace
- Hepatology Unit and Laboratory of Molecular Genetics and Pathology of Hepatitis Viruses, Pisa University Hospital, Pisa, Italy
| | - Ferruccio Bonino
- Biostructure and Bio-imaging Institute of National Research Council of Italy, Naples, Italy
| | - Maurizia Rossana Brunetto
- Department of Clinical and Experimental Medicine, University of Pisa, Pisa, Italy.,Hepatology Unit and Laboratory of Molecular Genetics and Pathology of Hepatitis Viruses, Pisa University Hospital, Pisa, Italy.,Biostructure and Bio-imaging Institute of National Research Council of Italy, Naples, Italy
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7
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Shubin AV, Demidyuk IV, Komissarov AA, Rafieva LM, Kostrov SV. Cytoplasmic vacuolization in cell death and survival. Oncotarget 2018; 7:55863-55889. [PMID: 27331412 PMCID: PMC5342458 DOI: 10.18632/oncotarget.10150] [Citation(s) in RCA: 202] [Impact Index Per Article: 33.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2016] [Accepted: 06/06/2016] [Indexed: 12/15/2022] Open
Abstract
Cytoplasmic vacuolization (also called cytoplasmic vacuolation) is a well-known morphological phenomenon observed in mammalian cells after exposure to bacterial or viral pathogens as well as to various natural and artificial low-molecular-weight compounds. Vacuolization often accompanies cell death; however, its role in cell death processes remains unclear. This can be attributed to studying vacuolization at the level of morphology for many years. At the same time, new data on the molecular mechanisms of the vacuole formation and structure have become available. In addition, numerous examples of the association between vacuolization and previously unknown cell death types have been reported. Here, we review these data to make a deeper insight into the role of cytoplasmic vacuolization in cell death and survival.
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Affiliation(s)
- Andrey V Shubin
- Laboratory of Protein Engineering, Institute of Molecular Genetics, Moscow, Russia.,Laboratory of Chemical Carcinogenesis, N.N. Blokhin Russian Cancer Research Center, Moscow, Russia.,Laboratory of Biologically Active Nanostructures, N.F. Gamaleya Institute of Epidemiology and Microbiology, Moscow, Russia
| | - Ilya V Demidyuk
- Laboratory of Protein Engineering, Institute of Molecular Genetics, Moscow, Russia
| | - Alexey A Komissarov
- Laboratory of Protein Engineering, Institute of Molecular Genetics, Moscow, Russia
| | - Lola M Rafieva
- Laboratory of Protein Engineering, Institute of Molecular Genetics, Moscow, Russia
| | - Sergey V Kostrov
- Laboratory of Protein Engineering, Institute of Molecular Genetics, Moscow, Russia
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8
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Zacchi LF, Wu HC, Bell SL, Millen L, Paton AW, Paton JC, Thomas PJ, Zolkiewski M, Brodsky JL. The BiP molecular chaperone plays multiple roles during the biogenesis of torsinA, an AAA+ ATPase associated with the neurological disease early-onset torsion dystonia. J Biol Chem 2014; 289:12727-47. [PMID: 24627482 PMCID: PMC4007462 DOI: 10.1074/jbc.m113.529123] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Revised: 03/09/2014] [Indexed: 01/02/2023] Open
Abstract
Early-onset torsion dystonia (EOTD) is a neurological disorder characterized by involuntary and sustained muscle contractions that can lead to paralysis and abnormal posture. EOTD is associated with the deletion of a glutamate (ΔE) in torsinA, an endoplasmic reticulum (ER) resident AAA(+) ATPase. To date, the effect of ΔE on torsinA and the reason that this mutation results in EOTD are unclear. Moreover, there are no specific therapeutic options to treat EOTD. To define the underlying biochemical defects associated with torsinAΔE and to uncover factors that might be targeted to offset defects associated with torsinAΔE, we developed a yeast torsinA expression system and tested the roles of ER chaperones in mediating the folding and stability of torsinA and torsinAΔE. We discovered that the ER lumenal Hsp70, BiP, an associated Hsp40, Scj1, and a nucleotide exchange factor, Lhs1, stabilize torsinA and torsinAΔE. BiP also maintained torsinA and torsinAΔE solubility. Mutations predicted to compromise specific torsinA functional motifs showed a synthetic interaction with the ΔE mutation and destabilized torsinAΔE, suggesting that the ΔE mutation predisposes torsinA to defects in the presence of secondary insults. In this case, BiP was required for torsinAΔE degradation, consistent with data that specific chaperones exhibit either pro-degradative or pro-folding activities. Finally, using two independent approaches, we established that BiP stabilizes torsinA and torsinAΔE in mammalian cells. Together, these data define BiP as the first identified torsinA chaperone, and treatments that modulate BiP might improve symptoms associated with EOTD.
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Affiliation(s)
- Lucía F. Zacchi
- From the Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - Hui-Chuan Wu
- the Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
| | - Samantha L. Bell
- From the Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - Linda Millen
- the Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, and
| | - Adrienne W. Paton
- the Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - James C. Paton
- the Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Philip J. Thomas
- the Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, and
| | - Michal Zolkiewski
- the Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
| | - Jeffrey L. Brodsky
- From the Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
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9
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Chang J, Guo JT, Du Y, Block T. Imino sugar glucosidase inhibitors as broadly active anti-filovirus agents. Emerg Microbes Infect 2013; 2:e77. [PMID: 26038444 PMCID: PMC3924557 DOI: 10.1038/emi.2013.77] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Revised: 09/16/2013] [Accepted: 09/22/2013] [Indexed: 12/12/2022]
Abstract
Ebola virus and Marburg virus are members of the family of Filoviridae and are etiological agents of a deadly hemorrhagic fever disease. The clinical symptoms of Ebola and Marburg hemorrhagic fevers are difficult to distinguish and there are currently no specific antiviral therapies against either of the viruses. Therefore, a drug that is safe and effective against both would be an enormous breakthrough. We and others have shown that the folding of the glycoproteins of many enveloped viruses, including the filoviruses, is far more dependent upon the calnexin pathway of protein folding than are most host glycoproteins. Drugs that inhibit this pathway would be expected to be selectively antiviral. Indeed, as we summarize in this review, imino sugars that are competitive inhibitors of the host endoplasmic reticular α-glucosidases I and II, which are enzymes that process N-glycan on nascent glycoproteins and thereby inhibit calnexin binding to the nascent glycoproteins, have been shown to have antiviral activity against a number of enveloped viruses including filoviruses. In this review, we describe the state of development of imino sugars for use against the filoviruses, and provide an explanation for the basis of their antiviral activity as well as limitations.
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Affiliation(s)
- Jinhong Chang
- The Department of Microbiology and Immunology, Drexel University College of Medicine , Doylestown, PA 18902, USA ; The Institute of Hepatitis and Virus Research , Doylestown, PA 18902, USA
| | - Ju-Tao Guo
- The Department of Microbiology and Immunology, Drexel University College of Medicine , Doylestown, PA 18902, USA ; The Institute of Hepatitis and Virus Research , Doylestown, PA 18902, USA
| | - Yanming Du
- The Institute of Hepatitis and Virus Research , Doylestown, PA 18902, USA
| | - Timothy Block
- The Department of Microbiology and Immunology, Drexel University College of Medicine , Doylestown, PA 18902, USA ; The Institute of Hepatitis and Virus Research , Doylestown, PA 18902, USA
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10
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Buti M, Rodríguez Frías F, Esteban R. [Quantification of hepatitis B virus HBsAg: clinical implications]. Med Clin (Barc) 2012; 138:483-8. [PMID: 21719049 DOI: 10.1016/j.medcli.2011.04.024] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2011] [Revised: 04/18/2011] [Accepted: 04/28/2011] [Indexed: 02/07/2023]
Abstract
The surface antigen of hepatitis B virus (HBsAg) is the main serological marker of HBV infection since its discovery almost 50 years ago. Currently the quantification of HBsAg has acquired special relevance as there are commercial tests to measure its levels. Several studies have shown that in patients treated with pegylated interferon alfa the fall of HBsAg levels predicts the loss of HBsAg and persistent virologic response. The role of the quantification of HBsAg in the treatment with nucleoside analogues is still not well understood and requires further studies.
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Affiliation(s)
- Maria Buti
- Servicio de Hepatología, Hospital Universitario Vall d'Hebron, Barcelona, Spain.
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11
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Novel evidence suggests Hepatitis B virus surface proteins participate in regulation of HBV genome replication. Virol Sin 2011; 26:131-8. [PMID: 21468936 DOI: 10.1007/s12250-011-3190-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2011] [Accepted: 03/02/2011] [Indexed: 12/13/2022] Open
Abstract
Naturally occurring mutations in surface proteins of Hepatitis B virus (HBV) usually result in altered hepatitis B surface antigen (HBsAg) secretion efficiency. In the present study, we reported two conserved residues, M75 and M103 with respect to HBsAg, mutations of which not only attenuated HBsAg secretion (M75 only), but also suppressed HBV genome replication without compromising the overlapping p-gene product. We also found M75 and M103 can initiate truncated surface protein (TSPs) synthesis upon over-expression of full-length surface proteins, which may possibly contribute to HBV genome replication. However, attempts to rescue replication-defective HBV mutant by co-expression of TSPs initiated from M75 or M103 were unsuccessful, which indicated surface proteins rather than the putative TSPs were involved in regulation of HBV genome replication.
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12
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Moucari R, Marcellin P. Quantification of hepatitis B surface antigen: a new concept for the management of chronic hepatitis B. Liver Int 2011; 31 Suppl 1:122-8. [PMID: 21205149 DOI: 10.1111/j.1478-3231.2010.02390.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
HBsAg is a very important clinical test that might not only indicate active hepatitis B virus (HBV) infection but might also be used to predict clinical and treatment outcome. Clearance of HBsAg in patients with chronic HBV infection is associated with a much better clinical outcome, although surveillance for early detection of hepatocellular carcinoma (HCC) should continue. HBV DNA quantification is currently used for selecting candidates for therapy, monitoring response to therapy and detecting the emergence of drug resistance. Assays for HBsAg quantification are less expensive than HBV DNA and fully automated with a high throughput capacity. HBsAg titering may be a useful tool to manage patients with chronic HBV, to more clearly define which patients may, and more importantly, may not, benefit from treatment. Baseline and on-treatment HBsAg quantification may help to refine future treatment algorithms for both immune-modulator therapy and nucleos(t)ide analogues. Both HBV markers provide complementary information on the status of HBV infection. However, the relevance of serum HBsAg levels and its use as a reliable replacement for both covalently closed circular DNA and HBV DNA remain unclear.
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Affiliation(s)
- Rami Moucari
- Hepatology Department and INSERM U773, Beaujon Hospital, Clichy, France.
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13
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Brunetto MR. A new role for an old marker, HBsAg. J Hepatol 2010; 52:475-7. [PMID: 20185190 DOI: 10.1016/j.jhep.2009.12.020] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/15/2009] [Revised: 12/18/2009] [Accepted: 12/24/2009] [Indexed: 01/04/2023]
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14
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Liu J, Yang Y, Hu B, Ma ZY, Huang HP, Yu Y, Liu SP, Lu MJ, Yang DL. Development of HBsAg-binding aptamers that bind HepG2.2.15 cells via HBV surface antigen. Virol Sin 2010; 25:27-35. [PMID: 20960281 DOI: 10.1007/s12250-010-3091-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2009] [Accepted: 10/09/2009] [Indexed: 10/19/2022] Open
Abstract
Hepatitis B virus surface antigen (HBsAg), a specific antigen on the membrane of Hepatitis B virus (HBV)-infected cells, provides a perfect target for therapeutic drugs. The development of reagents with high affinity and specificity to the HBsAg is of great significance to the early-stage diagnosis and treatment of HBV infection. Herein, we report the selection of RNA aptamers that can specifically bind to HBsAg protein and HBsAg-positive hepatocytes. One high affinity aptamer, HBs-A22, was isolated from an initial 115 mer library of ~1.1 x 10¹⁵ random-sequence RNA molecules using the SELEX procedure. The selected aptamer HBs-A22 bound specifically to hepatoma cell line HepG2.2.15 that expresses HBsAg but did not bind to HBsAg-devoid HepG2 cells. This is the first reported RNA aptamer which could bind to a HBV specific antigen. This newly isolated aptamer could be modified to deliver imaging, diagnostic, and therapeutic agents targeted at HBV-infected cells.
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Affiliation(s)
- Jia Liu
- Division of Clinical Immunology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
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15
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Ogunniyi AO, Story CM, Papa E, Guillen E, Love JC. Screening individual hybridomas by microengraving to discover monoclonal antibodies. Nat Protoc 2009; 4:767-82. [PMID: 19528952 DOI: 10.1038/nprot.2009.40] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The demand for monoclonal antibodies (mAbs) in biomedical research is significant, but the current methodologies used to discover them are both lengthy and costly. Consequently, the diversity of antibodies available for any particular antigen remains limited. Microengraving is a soft lithographic technique that provides a rapid and efficient alternative for discovering new mAbs. This protocol describes how to use microengraving to screen mouse hybridomas to establish new cell lines producing unique mAbs. Single cells from a polyclonal population are isolated into an array of microscale wells (approximately 10(5) cells per screen). The array is then used to print a protein microarray, where each element contains the antibodies captured from individual wells. The antibodies on the microarray are screened with antigens of interest, and mapped to the corresponding cells, which are then recovered from their microwells by micromanipulation. Screening and retrieval require approximately 1-3 d (9-12 d including the steps for preparing arrays of microwells).
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Affiliation(s)
- Adebola O Ogunniyi
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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16
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Wen WH, Qin WJ, Gao H, Zhao J, Jia LT, Liao QH, Meng YL, Jin BQ, Yao LB, Chen SY, Yang AG. An hepatitis B virus surface antigen specific single chain of variable fragment derived from a natural immune antigen binding fragment phage display library is specifically internalized by HepG2.2.15 cells. J Viral Hepat 2007; 14:512-9. [PMID: 17576393 DOI: 10.1111/j.1365-2893.2007.00843.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Hepatitis B virus surface antigen (HBsAg), a specific antigen on the membrane of hepatitis B virus (HBV)-infected cells, provides a perfect target for therapeutic drugs. In order to mediate successful targeted delivery of these therapies, it is essential to have antibodies that recognize HBsAg with high specificity and affinity. In this report, we constructed a natural immune antigen binding fragments (Fab) antibody phage display library against HBsAg and after three rounds of panning, five Fab fragments with significant HBsAg binding ability were selected and analysed. DNA sequencing revealed that all the light chains had the same sequence, while all the Fd genes exhibited different sequences. For further application, all of the Fab antibodies were reconstructed into single chain antibodies (scFvs) and expressed in Escherichia coli BL21 cells. Indirect enzyme-linked immunosorbent assay analysis demonstrated that all five scFvs maintained a high affinity for HBsAg and could bind HBsAg on the membrane of HBV-infected cells. Indirect fluorescent staining analysis revealed that one of the scFvs (scFv15) could be internalized into HBsAg-positive HepG2.2.15 cells through clathrin-mediated endocytosis pathway. The internalizing scFv15 antibody would have great potential for the targeted delivery of therapeutics to HBV-infected cells.
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Affiliation(s)
- W-H Wen
- State Key Laboratory of Cancer Biology, Department of Immunology, Fourth Military Medical University, Xi'an, China
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17
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Wen WH, Liu JY, Qin WJ, Zhao J, Wang T, Jia LT, Meng YL, Gao H, Xue CF, Jin BQ, Yao LB, Chen SY, Yang AG. Targeted inhibition of HBV gene expression by single-chain antibody mediated small interfering RNA delivery. Hepatology 2007; 46:84-94. [PMID: 17596868 DOI: 10.1002/hep.21663] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
Abstract
UNLABELLED RNA interference is highly effective at inhibiting HBV gene expression and replication. However, before small interfering RNA (siRNA) can be used in the clinic, it is essential to develop a system to target their delivery. Antibody-mediated delivery is a novel approach for targeting siRNA to appropriate cells. In this report, we asked whether this siRNA delivery strategy would be effective against HBV. Of 5 candidates, a specific siRNA that effectively inhibited HBV gene expression and replication was determined. Two fusion proteins, s-tP and sCkappa-tP, were constructed to contain a single chain of the human variable fragment, scFv, against hepatitis B surface antigen (HBsAg), a truncated protamine (tP), and in the case of sCkappa-tP, a constant region of the kappa chain (Ckappa). S-tP and sCkappa-tP were developed to provide targeted delivery of the siRNA, siRNA expressing cassettes (SEC), and siRNA-producing plasmids. Fluorescein isothiocyanate-siRNA, fluorescein isothiocyanate-SEC, and plasmid DNA were specifically delivered into HBsAg-positive cells using the sCkappa-tP fusion protein, and effectively inhibited HBV gene expression and replication. HBV gene expression was also inhibited by siRNA or siRNA-producing plasmids in HBV transgenic mice. CONCLUSION Our results describe a potential method for the targeted delivery of siRNA or siRNA-producing plasmids against HBV, using anti-HBsAg fusion proteins.
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Affiliation(s)
- Wei-Hong Wen
- State Key Laboratory of Cancer Biology, Department of Immunology, Xijing Hospital, Fourth Military Medical University, Xi'an, China
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18
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Rong Q, Huang J, Su E, Li J, Li J, Zhang L, Cao K. Infection of hepatitis B virus in extrahepatic endothelial tissues mediated by endothelial progenitor cells. Virol J 2007; 4:36. [PMID: 17407553 PMCID: PMC1851702 DOI: 10.1186/1743-422x-4-36] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2007] [Accepted: 04/02/2007] [Indexed: 12/22/2022] Open
Abstract
Background Hepatitis B virus (HBV) replication has been reported to be involved in many extrahepatic viral disorders; however, the mechanism by which HBV is trans-infected into extrahepatic tissues such as HBV associated myocarditis remains largely unknown. Results In this study, we showed that human cord blood endothelial progenitor cells (EPCs), but not human umbilical vein endothelial cells (HUVECs) could be effectively infected by uptake of HBV in vitro. Exposure of EPCs with HBV resulted in HBV DNA and viral particles were detected in EPCs at day 3 after HBV challenge, which were peaked around day 7 and declined in 3 weeks. Consistently, HBV envelope surface and core antigens were first detected in EPCs at day 3 after virus challenge and were retained to be detectable for 3 weeks. In contrast, HBV covalently closed circular DNA was not detected in EPCs at any time after virus challenge. Intravenous transplantation of HBV-treated EPCs into myocardial infarction and acute renal ischemia mouse model resulted in incorporation of HBV into injured heart, lung, and renal capillary endothelial tissues. Conclusion These results strongly support that EPCs serve as virus carrier mediating HBV trans-infection into the injured endothelial tissues. The findings might provide a novel mechanism for HBV-associated myocarditis and other HBV-related extrahepatic diseases as well.
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Affiliation(s)
- Qifei Rong
- Department of Cardiology, First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, People's Republic of China
| | - Jun Huang
- Department of Cardiology, First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, People's Republic of China
| | - Enben Su
- Department of Cardiology, First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, People's Republic of China
| | - Jun Li
- Department of Infectious Disease, First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, People's Republic of China
| | - Jianyong Li
- Department of Hematology, First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, People's Republic of China
| | - Lili Zhang
- Department of Infectious Disease, First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, People's Republic of China
| | - Kejiang Cao
- Department of Cardiology, First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, People's Republic of China
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19
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Patient R, Hourioux C, Sizaret PY, Trassard S, Sureau C, Roingeard P. Hepatitis B virus subviral envelope particle morphogenesis and intracellular trafficking. J Virol 2007; 81:3842-51. [PMID: 17267490 PMCID: PMC1866106 DOI: 10.1128/jvi.02741-06] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Hepatitis B virus (HBV) is unusual in that its surface proteins (small [S], medium, and large [L]) are not only incorporated into the virion envelope but they also bud into empty subviral particles in great excess over virions. The morphogenesis of these subviral envelope particles remains unclear, but the S protein is essential and sufficient for budding. We show here that, in contrast to the presumed model, the HBV subviral particle formed by the S protein self-assembles into branched filaments in the lumen of the endoplasmic reticulum (ER). These long filaments are then folded and bridged for packing into crystal-like structures, which are then transported by ER-derived vesicles to the ER-Golgi intermediate compartment (ERGIC). Within the ERGIC, they are unpacked and relaxed, and their size and shape probably limits further progression through the secretory pathway. Such progression requires their conversion into spherical particles, which occurred spontaneously during the purification of these filaments by affinity chromatography. Small branched filaments are also formed by the L protein in the ER lumen, but these filaments are not packed into transport vesicles. They are transported less efficiently to the ERGIC, potentially accounting for the retention of the L protein within cells. These findings shed light on an important step in the HBV infectious cycle, as the intracellular accumulation of HBV subviral filaments may be directly linked to viral pathogenesis.
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Affiliation(s)
- Romuald Patient
- Université François Rabelais, INSERM ERI 19, Laboratoire de Biologie Cellulaire, Faculté de Médecine de Tours, 10 boulevard Tonnellé, F-37032 Tours Cedex, France
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20
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Bugarcic A, Taylor JA. Rotavirus nonstructural glycoprotein NSP4 is secreted from the apical surfaces of polarized epithelial cells. J Virol 2006; 80:12343-9. [PMID: 17035333 PMCID: PMC1676281 DOI: 10.1128/jvi.01378-06] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
NSP4, a nonstructural glycoprotein encoded by rotavirus, is involved in the morphogenesis of virus particles in the endoplasmic reticulum of infected cells. NSP4 is also implicated in the pathophysiology of rotavirus-induced diarrhea by acting as an enterotoxin. To mediate enterotoxic effects in vivo, NSP4 must be secreted or released from rotavirus-infected cells in a soluble form; however, previous studies have indicated that NSP4 is a transmembrane glycoprotein localized within endomembrane compartments in infected cells. In this study, we examined the fate of NSP4 synthesized in Caco-2 cells infected with bovine rotavirus. Our studies reveal that NSP4 is actively secreted into the culture medium, preferentially from the infected-cell apical surface. The secretion of NSP4 is dramatically inhibited by brefeldin A and monensin, suggesting that a Golgi-dependent pathway is involved in release of the protein. In agreement with the proposed involvement of the Golgi apparatus during secretion, secreted NSP4 appears to undergo additional posttranslational modification compared to its cell-associated counterpart and is partially resistant to deglycosylation by endoglycosidase H. Our experiments identify a novel, soluble form of NSP4 secreted from virus-infected cells with the potential to carry out the enterotoxigenic role previously attributed to recombinant forms of the protein.
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Affiliation(s)
- Andrea Bugarcic
- School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
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21
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Blanchet M, Sureau C. Analysis of the cytosolic domains of the hepatitis B virus envelope proteins for their function in viral particle assembly and infectivity. J Virol 2006; 80:11935-45. [PMID: 17020942 PMCID: PMC1676254 DOI: 10.1128/jvi.00621-06] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The hepatitis B virus (HBV) envelope proteins have the ability to assemble three types of viral particles, (i) the empty subviral particles (SVPs), (ii) the mature HBV virions, and (iii) the hepatitis delta virus (HDV) particles, in cells that are coinfected with HBV and HDV. To gain insight into the function of the HBV envelope proteins in morphogenesis of HBV or HDV virions, we have investigated subdomains of the envelope proteins that have been shown or predicted to lie at the cytosolic face of the endoplasmic reticulum membrane during synthesis, a position prone to interaction with the inner core structure. These domains, referred to here as cytosolic loops I and II (CYL-I and -II, respectively), were subjected to mutagenesis. The mutations were introduced in the three HBV envelope proteins, designated small, middle, and large (S-HBsAg, M-HBsAg, and L-HBsAg, respectively). The mutants were expressed in HuH-7 cells to evaluate their capacity for self-assembly and formation of HBV or HDV virions when HBV nucleocapsid or HDV ribonucleoprotein, respectively, was provided. We found that SVP-competent CYL-I mutations between positions 23 and 78 of the S domain were permissive to HBV or HDV virion assembly. One mutation (P29A) was permissive for synthesis of the S- and M-HBsAg but adversely affected the synthesis or stability of L-HBsAg, thereby preventing the assembly of HBV virions. Furthermore, using an in vitro infection assay based on the HepaRG cells and the HDV model, we have shown that particles coated with envelope proteins bearing CYL-I mutations were fully infectious, hence indicating the absence of an infectivity determinant in this region. Finally, we demonstrated that the tryptophan residues at positions 196, 199, and 201 in CYL-II, which were shown to exert a matrix function for assembly of HDV particles (I. Komla-Soukha and C. Sureau, J. Virol. 80:4648-4655, 2006), were dispensable for both assembly and infectivity of HBV virions.
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Affiliation(s)
- Matthieu Blanchet
- Laboratoire de Virologie, Institut National de la Transfusion Sanguine, 6 rue Alexandre Cabanel, 75739 Paris, France
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22
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Abstract
The hepatitis delta virus (HDV) is a subviral agent that utilizes the envelope proteins of the hepatitis B virus (HBV) for propagation. When introduced into permissive cells, the HDV RNA genome replicates and associates with multiple copies of the HDV-encoded proteins to assemble a ribonucleoprotein (RNP) complex. The mechanism necessary to export the RNP from the cell is provided by the HBV envelope proteins, which have the capacity to assemble lipoprotein vesicles that bud into the lumen of a pre-Golgi compartment before being secreted. In addition to allowing the release of the HDV RNP, the HBV envelope proteins also provide a means for its targeting to an uninfected cell, thereby ensuring the spread of HDV. This chapter covers the molecular aspects of the HBV envelope protein functions in the HDV replication cycle, in particular the activity of the small envelope protein in RNP export and the function of the large envelope protein at viral entry.
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Affiliation(s)
- C Sureau
- Laboratoire de Virologie Moléculaire, Institut National de la Transfusion Sanguine, Paris, France.
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23
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Yu D, Fukuda T, Kuroda S, Tanizawa K, Kondo A, Ueda M, Yamada T, Tada H, Seno M. Engineered bio-nanocapsules, the selective vector for drug delivery system. IUBMB Life 2006; 58:1-6. [PMID: 16596748 DOI: 10.1080/15216540500484368] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The bio-nanocapsule (BNC) is our concept of artificial hollow nanoparticles that have been designed and produced through biotechnological procedures. We proposed an empty virus-like particle, which consists of a recombinant L envelope protein of hepatitis B virus (HBV) and a lipid derived from the host cell, as an engineered BNC. Although this BNC was first developed as an immunogen of hepatitis B vaccine, the pre-S1 region in N-terminus of L envelope protein confers hepatocyte specific infectivity of HBV on the BNC. This recombinant BNC is now being developed as a novel platform of drug delivery system (DDS) vector for selective delivery.
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Affiliation(s)
- Dongwei Yu
- Graduate School of Natural Science and Technology, Okayama University, 3.1.1 Tsushima-Naka, Okayama 700-8530, Japan
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24
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Abstract
This chapter describes the interactions between the different structural components of the viruses and discusses their relevance for the process of virion formation. Two key factors determine the efficiency of the assembly process: intracellular transport and molecular interactions. Many viruses have evolved elaborate strategies to ensure the swift and accurate delivery of the virion components to the cellular compartment(s) where they must meet and form (sub) structures. Assembly of viruses starts in the nucleus by the encapsidation of viral DNA, using cytoplasmically synthesized capsid proteins; nucleocapsids then migrate to the cytosol, by budding at the inner nuclear membrane followed by deenvelopment, to pick up the tegument proteins.
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Affiliation(s)
- Cornelis A M de Haan
- Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, 3584 CL Utrecht, The Netherlands
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25
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Lambert C, Thomé N, Kluck CJ, Prange R. Functional incorporation of green fluorescent protein into hepatitis B virus envelope particles. Virology 2005; 330:158-67. [PMID: 15527842 PMCID: PMC7111749 DOI: 10.1016/j.virol.2004.09.031] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2004] [Revised: 08/13/2004] [Accepted: 09/20/2004] [Indexed: 12/22/2022]
Abstract
The envelope of hepatitis B virus (HBV), containing the L, M, and S proteins, is essential for virus entry and maturation. For direct visualization of HBV, we determined whether envelope assembly could accommodate the green fluorescent protein (GFP). While the C-terminal addition of GFP to S trans-dominant negatively inhibited empty envelope particle secretion, the N-terminal GFP fusion to S (GFP.S) was co-integrated into the envelope, giving rise to fluorescent particles. Microscopy and topogenesis analyses demonstrated that the proper intracellular distribution and folding of GFP.S, required for particle export were rescued by interprotein interactions with wild-type S. Thereby, a dual location of GFP, inside and outside the envelope, was observed. GFP.S was also efficiently packaged into the viral envelope, and these GFP-tagged virions retained the capacity for attachment to HBV receptor-positive cells in vitro. Together, GFP-tagged virions should be suitable to monitor HBV uptake and egress in live hepatocytes.
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Affiliation(s)
- Carsten Lambert
- Department of Medical Microbiology and Hygiene, University of Mainz, D-55101 Mainz, Germany
| | - Nicole Thomé
- Department of Medical Microbiology and Hygiene, University of Mainz, D-55101 Mainz, Germany
| | - Christoph J. Kluck
- Biochemistry Center, University of Heidelberg, D-69120 Heidelberg, Germany
| | - Reinhild Prange
- Department of Medical Microbiology and Hygiene, University of Mainz, D-55101 Mainz, Germany
- Corresponding author. Mailing address: Institute for Medical Microbiology and Hygiene, University of Mainz, Augustusplatz, D-55101 Mainz, Germany. Fax: +49 6131 3932359.
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26
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Abstract
The hepatitis B virus (HBV) is an enveloped DNA virus with an icosahedral capsid replicating via reverse transcription. The crystal structure of the capsid is known. It has a diameter of 36 nm and is formed by one protein species (C protein). The viral envelope contains three different coterminal proteins (S, M, and L proteins) spanning the membrane several times. These proteins are not only released from infected cells as components of the viral envelope but in 10,000-fold excess as subviral lipoprotein particles with a diameter of 22 nm containing no capsid. Assembly of the capsid occurs in the cytosol and results in packaging of a 3.5 kb RNA molecule together with viral and cellular factors. This newly formed capsid cannot be enveloped. Rather, synthesis of the viral DNA genome in the lumen of the capsid by reverse transcription is required to induce a budding competent state. Envelopment then takes place at an intracellular membrane of the pre-Golgi compartment. The S and the L protein, but not the M protein, is required for this process. The L protein forms two different transmembrane topologies. The isoform exposing the N-terminal part at the cytosolic side of the membrane is essential for budding. In this domain, a 22 amino acid (aa) long linear stretch has been mapped genetically to play a vital role in the morphogenetic process. This domain probably mediates the contact to the capsid. A second matrix domain was mapped to the cytosolic loop of the S protein. A similar genetic approach identified two small areas on the capsid surface, which might interact with the envelope proteins during envelopment.
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Affiliation(s)
- Volker Bruss
- Department of Virology, University of Göttingen, Kreuzbergring 57, 37075 Göttingen, Germany.
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27
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Lambert C, Prange R. Development and characterization of a 293 cell line with regulatable expression of the hepatitis B virus large envelope protein. J Virol Methods 2004; 121:181-90. [PMID: 15381355 DOI: 10.1016/j.jviromet.2004.06.018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2004] [Revised: 06/16/2004] [Accepted: 06/21/2004] [Indexed: 11/23/2022]
Abstract
During the life cycle of hepatitis B virus (HBV) the large L envelope protein plays a pivotal role that is related to its peculiar dual transmembrane topology. To study the complex structure and diverse functions of L under regulated conditions of production, a human 293 cell line stably expressing L under the control of the ecdysone-inducible promoter was generated. Cells demonstrated stringent dose- and time-dependent kinetics of induction with undetectable background expression in the absence of the inducer. Temporal control of L expression allowed to trace (i) its posttranslational reorientation resulting in the mixed topology; (ii) its spatial redistribution from the endoplasmic reticulum to Golgi-like structures; and (iii) its intracellular retention in a membrane-associated configuration. On regulated overproduction, L blocked the secretion of HBV small envelope polypeptides without impairing the cell secretory apparatus. Despite the continuous high-level storage of L within the 293 cell line, no cytopathic effects could be detected. This is in contrast to ground-glass hepatocytes of chronic HBV carriers and HBV transgenic mice and may imply that the intracellular storage of L is particularly damaging to the liver cell.
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Affiliation(s)
- Carsten Lambert
- Department of Medical Microbiology and Hygiene, University of Mainz, Augustusplatz, 55101 Mainz, Germany
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28
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Yoshii K, Konno A, Goto A, Nio J, Obara M, Ueki T, Hayasaka D, Mizutani T, Kariwa H, Takashima I. Single point mutation in tick-borne encephalitis virus prM protein induces a reduction of virus particle secretion. J Gen Virol 2004; 85:3049-3058. [PMID: 15448368 DOI: 10.1099/vir.0.80169-0] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Flaviviruses are assembled to bud into the lumen of the endoplasmic reticulum (ER) and are secreted through the vesicle transport pathway. Virus envelope proteins play important roles in this process. In this study, the effect of mutations in the envelope proteins of tick-borne encephalitis (TBE) virus on secretion of virus-like particles (VLPs), using a recombinant plasmid expression system was analysed. It was found that a single point mutation at position 63 in prM induces a reduction in secretion of VLPs. The mutation in prM did not affect the folding of the envelope proteins, and chaperone-like activity of prM was maintained. As observed by immunofluorescence microscopy, viral envelope proteins with the mutation in prM were scarce in the Golgi complex, and accumulated in the ER. Electron microscopic analysis of cells expressing the mutated prM revealed that many tubular structures were present in the lumen. The insertion of the prM mutation at aa 63 into the viral genome reduced the production of infectious virus particles. This data suggest that prM plays a crucial role in the virus budding process.
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Affiliation(s)
- Kentarou Yoshii
- Laboratory of Public Health, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
| | - Akihiro Konno
- Laboratory of Anatomy, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
| | - Akiko Goto
- Laboratory of Public Health, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
| | - Junko Nio
- Laboratory of Anatomy, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
| | - Mayumi Obara
- Laboratory of Public Health, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
| | - Tomotaka Ueki
- Laboratory of Public Health, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
| | - Daisuke Hayasaka
- Department of Pathology, Institute of Tropical Medicine, Nagasaki University, 1-12-4 Sakamoto, Nagasaki 852-8523, Japan
| | - Tetsuya Mizutani
- Laboratory of Public Health, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
| | - Hiroaki Kariwa
- Laboratory of Public Health, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
| | - Ikuo Takashima
- Laboratory of Public Health, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
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29
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Lin YL, Shiao MS, Mettling C, Chou CK. Cholesterol requirement of hepatitis B surface antigen (HBsAg) secretion. Virology 2003; 314:253-60. [PMID: 14517078 DOI: 10.1016/s0042-6822(03)00403-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Hepatitis B virus-infected patients secrete enormous quantities (50-300 microg/ml) of hepatitis B surface antigen (HBsAg) in their serum. One hypothesis for this synthetic effort is that these lipoprotein particles serve to adsorb neutralizing antisurface antibodies. We have shown that insulin suppresses the expression of HBsAg in human hepatoma cell Hep3B cells. We further studied the signaling pathway of insulin on the inhibition of HBsAg. Using a fungal metabolite, lovastatin, to block the p21Ras signaling pathway of insulin, we found that lovastatin inhibited the secretion of HBsAg into culture medium in Hep3B cells; however, the involvement of p21Ras-MAPKs was excluded in this effect. The cholesterol depletion from the membrane, leading to the destabilization of rafts, was the mechanism for the lovastatin inhibition of HBsAg secretion. However, lovastatin has no effect on the secretion of infectious viral Dane particles. Herein, we show for the first time that cholesterol is required for HBsAg secretion.
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Affiliation(s)
- Yea-Lih Lin
- Institut de Génétique Humaine, IGH-CNRS, 141, rue de la Cardonille, 34396 Montpellier Cedex 5, France.
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Smith ML, Richter L, Arntzen CJ, Shuler ML, Mason HS. Structural characterization of plant-derived hepatitis B surface antigen employed in oral immunization studies. Vaccine 2003; 21:4011-21. [PMID: 12922138 DOI: 10.1016/s0264-410x(03)00268-8] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Several subunit vaccine antigens have been successfully expressed in plants and recently the hepatitis B surface antigen (HBsAg), expressed in potatoes, was shown to be orally immunogenic in animal studies. However, to date, a detailed analysis of the plant-derived antigen is lacking. Herein, we comprehensively characterize the structure and post-translational processing of HBsAg from potato tuber and two plant cell suspension cultures. The HBsAg was found to accumulate intracellularly as tubular structures, with a complex size distribution, differing substantially from the virus-like particle (VLP) preparations of the current commercial vaccines. Extensive disulfide-bond cross-linking, which is important for immunogenicity, was evident and 21-37% of total HBsAg protein displayed epitopes which correlate with vaccine potency. The significance of these results with regard to the production of cost-effective orally delivered vaccines is discussed.
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Affiliation(s)
- Mark L Smith
- Department of Chemical Engineering, Cornell University, Ithaca, NY 14853, USA
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31
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Sojikul P, Buehner N, Mason HS. A plant signal peptide-hepatitis B surface antigen fusion protein with enhanced stability and immunogenicity expressed in plant cells. Proc Natl Acad Sci U S A 2003; 100:2209-14. [PMID: 12601177 PMCID: PMC151319 DOI: 10.1073/pnas.0438037100] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2002] [Accepted: 12/31/2002] [Indexed: 11/18/2022] Open
Abstract
The use of transgenic plants to express orally immunogenic protein antigens is an emerging strategy for vaccine biomanufacturing and delivery. This concept has particular suitability for developing countries. One factor that has limited the development of this technology is the relatively modest levels of accumulation of some antigenic proteins in plant tissues. We used fusion protein design to improve expression of the hepatitis B surface antigen (HBsAg) by attempting to mimic the process of HBsAg targeting to the endoplasmic reticulum of human liver cells during hepatitis B virus infection. We created a gene encoding a recombinant HBsAg modified to contain a plant signal peptide fused to its amino terminus. The signal peptide from soybean vegetative storage protein vspA (VSP alpha S) directed endoplasmic reticulum targeting of HBsAg in plant cells, but was not cleaved and resulted in enhanced VSP alpha S-HBsAg fusion accumulation. This product was more stable and presented the protective "a" antigenic determinant to significantly higher levels than unmodified native HBsAg expressed in plant cells. It also showed a greater extent of intermolecular disulfide bond formation and formation of virus-like particles. Moreover, VSP alpha S-HBsAg stimulated higher levels of serum IgG than native HBsAg when injected into mice. We conclude that HBsAg tolerates a polypeptide fusion at the amino terminus and that VSP alpha S-HBsAg is an improved antigen for plant-based expression of a subunit vaccine for hepatitis B virus.
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Affiliation(s)
- Punchapat Sojikul
- Department of Plant Biology, Cornell University and the Boyce Thompson Institute for Plant Research, Inc., Ithaca, NY 14853-1801, USA
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32
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Abdulkarim AS, Cao H, Huang B, McNiven MA. The large GTPase dynamin is required for hepatitis B virus protein secretion from hepatocytes. J Hepatol 2003; 38:76-83. [PMID: 12480563 DOI: 10.1016/s0168-8278(02)00326-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
BACKGROUND/AIMS The hepatocellular transport pathways and cellular proteins utilized during the packaging and secretion of hepatitis B virus are poorly understood. In this study, we tested if the large GTPase dynamin, a protein involved in vesicle formation and secretion at the trans-Golgi network in hepatocytes, is also used by hepatitis B virus (HBV) in secreting viral proteins. METHODS Using HepG2.2.15 cells expressing the full-length HBV genome, we tested the effects of wild-type and mutant dynamin on the localization and secretion of two hepatitis B antigens, hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg). Distribution of these two antigens was analyzed morphologically in cells transiently transfected with wild-type or mutant dynamin constructs, whereas secretion of the antigens was measured by testing for antigen levels in the media of transfected cells. RESULTS Mutant dynamin was found to induce a striking redistribution of HBsAg and HBeAg to a perinuclear compartment, as well as a decrease in the levels of HBsAg and HBeAg present in cell culture media indicating a reduction in viral protein secretion. At the electron microscopy level, cells expressing the mutant dynamin showed a marked accumulation of viral particles in dilated cisternae of an uncharacterized cellular compartment. CONCLUSIONS Intact dynamin function is required for secretion of HBV proteins from hepatocytes through an uncharacterized cellular compartment.
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Affiliation(s)
- Ahmad S Abdulkarim
- Center for Basic Research in Digestive Diseases and Department of Biochemistry and Molecular Biology, Mayo Clinic and Foundation, 200 First Street SW, Rochester, MN 55905, USA
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33
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Lewin S, Walters T, Locarnini S. Hepatitis B treatment: rational combination chemotherapy based on viral kinetic and animal model studies. Antiviral Res 2002; 55:381-96. [PMID: 12206877 DOI: 10.1016/s0166-3542(02)00071-2] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Hepatitis B virus (HBV) causes a generally non-cytopathic infection in the liver. Even though HBV is a DNA virus, it replicates via reverse transcription which is coordinated within the viral nucleocapsid by the virus-specific polymerase. The major transcriptional template is the viral mimichromosome from which the viral DNA exists as a covalently closed circular (ccc) molcule. The virus infects hepatocytes but can also be found in non-hepatocyte reservoirs such as bile-duct epithelium, mesangial cells of the kidney, pancreatic islet cells and lymphoid cells. When patients infected with HBV are treated with either interferon alpha or lamivudine, responses are variable and unpredictable. Sophisticated mathematical models analysing the dynamics of viral clearance during antiviral therapy have recently been applied to chronic hepatitis B. Typically complex profiles, rather than the usual biphasic responses seen with other diseases have been observed, indicating that antiviral efficacy requires substantila improvement. This may be achieved with combination chemotherapy. However, chronic hepatitis B is a complex and heterogeneous disease entity, and the challenge for the future is to define measurable end-points of treatment and address key virological issues such as the role of cccDNA and extra-hepatocyte replication in treatment failure. Clearly, new therapies and effective combination therapy protocols are urgently required in order to improve the present poor response rates in patients undergoing treatment.
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Affiliation(s)
- Sharon Lewin
- Victorian Infectious Diseases Service, Royal Melbourne Hospital, Department of Microbiology and Immunology, The University of Melbourne, Parkville, Australia
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Papatheodoridis GV, Dimou E, Papadimitropoulos V. Nucleoside analogues for chronic hepatitis B: antiviral efficacy and viral resistance. Am J Gastroenterol 2002; 97:1618-28. [PMID: 12135009 DOI: 10.1111/j.1572-0241.2002.05819.x] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Nucleoside analogues have been recently introduced in the management of chronic hepatitis B virus (HBV) infection. They mainly act by inhibition of HBV polymerase activity resulting in decrease of viral replication. They are administered orally, and most of them have an excellent tolerance and safety profile. Lamivudine is the only nucleoside analogue licensed for chronic hepatitis B. It has potent activity against HBV, and a 12-month course achieves clearance of hepatitis B e antigen (HBeAg) in 20-30% of HBeAg-positive patients and both biochemical and virological remission in more than 65-70% of HBeAg-negative chronic hepatitis B patients. Famciclovir and ganciclovir are less effective, whereas other nucleoside or nucleotide analogues, such as adefovir, entecavir, and emtricitabine, are currently under evaluation. Prolonged effective antiviral therapy is required for eradication of chronic HBV infection, but long-term treatment with nucleoside analogues has been found to be associated with progressively increasing rates of viral resistance because of emergence of resistant HBV mutant strains. Virological breakthroughs usually develop after the first 6 months of lamivudine monotherapy, and their rate ranges between 15% and 30% at 12 months and exceeds 50% after 3 yr of therapy. Resistant HBV mutant strains harbor point mutations in the HBV polymerase gene and predominantly in the well-conserved YMDD motif. Although resistant HBV strains may have impaired replication capacity compared with the wild HBV, their clinical significance has not been completely clarified yet. No significant biochemical or clinical event may develop in some cases, whereas severe biochemical breakthroughs with or without deterioration of liver function may develop in others. To date, there is no proven effective therapy for the resistant HBV mutant strains, although adefovir and entecavir seem to be interesting candidates.
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35
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Tai PC, Suk FM, Gerlich WH, Neurath AR, Shih C. Hypermodification and immune escape of an internally deleted middle-envelope (M) protein of frequent and predominant hepatitis B virus variants. Virology 2002; 292:44-58. [PMID: 11878907 DOI: 10.1006/viro.2001.1239] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Naturally occurring deletions within the human hepatitis B virus (HBV) preS2 region have frequently been identified in patients with hepatocellular carcinoma (HCC), while chronic carriers without cirrhosis and HCC contain no detectable preS2 deletion variants. We have characterized two different preS2 internal deletion variants from two patients. In addition to several weak phenotypes, our study revealed three unexpected strong phenotypes: (1) a paradoxical "hypermodification" phenomenon was observed with significantly increased size heterogeneity and molecular weights of the secreted middle (M) envelope proteins containing a preS2 internal deletion. This phenomenon was observed in transient transfection with a human hepatoma Huh7 cell line as well as in stable transfection with a rodent hepatoma cell line 7777. (2) A significantly increased intracellular accumulation of all three envelope proteins (large, middle, and small) was detected by both Western blot analysis and immunofluorescence microscopy. (3) The middle envelope proteins with a preS2 internal deletion were not recognized in vitro by a putative neutralizing antiserum, suggesting that these variants can evade immune recognition in vivo. To our knowledge, this is the first identification and characterization of the M deletion variant protein in HBV natural infection.
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Affiliation(s)
- Pei-Ching Tai
- Center for Tropical Diseases, University of Texas Medical Branch, Galveston, Texas, 77555-0609, USA
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36
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de Haan CA, Vennema H, Rottier PJ. Assembly of the coronavirus envelope: homotypic interactions between the M proteins. J Virol 2000; 74:4967-78. [PMID: 10799570 PMCID: PMC110848 DOI: 10.1128/jvi.74.11.4967-4978.2000] [Citation(s) in RCA: 141] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The viral membrane proteins M and E are the minimal requirements for the budding of coronavirus particles. Since the E protein occurs in particles only in trace amounts, the lateral interactions between the M proteins apparently generate the major driving force for envelope formation. By using coimmunoprecipitation and envelope incorporation assays, we provide extensive evidence for the existence of such M-M interactions. In addition, we determined which domains of the M protein are involved in this homotypic association, using a mutagenetic approach. Mutant M proteins which were not able to assemble into viruslike particles (VLPs) by themselves (C. A. M. de Haan, L. Kuo, P. S. Masters, H. Vennema, and P. J. M. Rottier, J. Virol. 72:6838-6850, 1998) were tested for the ability to associate with other M proteins and to be rescued into VLPs formed by assembly-competent M proteins. We found that M proteins lacking parts of the transmembrane cluster, of the amphipathic domain, or of the hydrophilic carboxy-terminal tail, or M proteins that had their luminal domain replaced by heterologous ectodomains, were still able to associate with assembly-competent M proteins, resulting in their coincorporation into VLPs. Only a mutant M protein in which all three transmembrane domains had been replaced lost this ability. The results indicate that M protein molecules interact with each other through multiple contact sites, particularly at the transmembrane level. Finally, we tested the stringency with which membrane proteins are selected for incorporation into the coronavirus envelope by probing the coassembly of some foreign proteins. The observed efficient exclusion from budding of the vesicular stomatitis virus G protein and the equine arteritis virus M protein indicates that envelope assembly is indeed a highly selective sorting process. The low but detectable incorporation of CD8 molecules, however, demonstrated that this process is not perfect.
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Affiliation(s)
- C A de Haan
- Institute of Virology, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, and Institute of Biomembranes, Utrecht University, 3584 CL Utrecht, The Netherlands
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37
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Fu J, VanDusen WJ, Kolodin DG, O'Keefe DO, Herber WK, George HA. Continuous culture study of the expression of hepatitis B surface antigen and its self-assembly into virus-like particles in Saccharomyces cerevisiae. Biotechnol Bioeng 2000; 49:578-86. [DOI: 10.1002/(sici)1097-0290(19960305)49:5<578::aid-bit11>3.0.co;2-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Abstract
This chapter focuses on the work carried out with tick-borne encephalitis (TBE) virus, the structurally best characterized of the flaviviruses. The data is related to those obtained with other flaviviruses, which are assumed to have a conserved structural organization, and compare the characteristics of flavivirus fusion to those of other enveloped viruses. Fusion proteins from several different virus families, including Orthomyxoviridae , Paramyxoviridae , Retroviridae , and Filoviridae have been shown to exhibit striking structural similarities; they all use a common mechanism for inducing membrane fusion, and the same general model applies to all of these cases. The flavivirus genome is a positive-stranded RNA molecule consisting of a single, long open reading frame of more than 10,000 nucleotides flanked by noncoding regions at the 5′ and 3′ ends. The fusion properties of flaviviruses have been investigated using several different assay systems, including virus-induced cell–cell fusion and virus–liposome fusion. All of these studies indicate that flaviviruses require an acidic pH for fusion, consistent with their proposed mode of entry.
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Affiliation(s)
- F X Heinz
- Institute of Virology, University of Vienna, Austria
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39
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Glenn JS, Marsters JC, Greenberg HB. Use of a prenylation inhibitor as a novel antiviral agent. J Virol 1998; 72:9303-6. [PMID: 9765479 PMCID: PMC110351 DOI: 10.1128/jvi.72.11.9303-9306.1998] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/1998] [Accepted: 07/24/1998] [Indexed: 12/18/2022] Open
Abstract
No specific therapy exists for hepatitis delta virus (HDV), which can cause severe liver disease. Molecular genetic studies have implicated the prenylation site of large delta antigen as a critical determinant of HDV particle assembly. We have established a cell culture model which produces HDV-like particles, and we show that delta antigen prenylation can be pharmacologically inhibited by the prenylation inhibitor BZA-5B. Furthermore, BZA-5B specifically abolishes particle production in a dose-dependent manner. These results demonstrate that the use of such a prenylation inhibitor-based antiviral therapy may be feasible and identify a novel class of potential antiviral agents.
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Affiliation(s)
- J S Glenn
- Division of Gastroenterology, Stanford University School of Medicine and Veterans Administration Medical Center, Palo Alto, California 94305-5487, USA.
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40
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Abstract
The hepatitis B virus (HBV) and other members of the hepadnaviridae replicate by reverse transcription of an RNA intermediate, pregenomic RNA (pgRNA). pgRNA is also translated into core protein and polymerase (reverse transcriptase) protein. Before being reverse transcribed, pgRNA is sequestrated from the cytoplasm by being packaged, together with polymerase, into subviral particles composed of core protein. For pgRNA to be encapsidated, its 5' end is folded into a stem-loop structure, known as the encapsidation signal or epsilon (epsilon). This stable bipartite stem-loop structure contains a bulge and an apical loop. Besides encapsidation, epsilon is involved in the activation of polymerase, in template restriction and in the initiation of DNA synthesis by reverse transcription. HBV DNA encoding epsilon forms part of the template that is translated into the precore/core fusion protein that is in turn post-translationally modified to produce hepatitis B e antigen (HBeAg). The DNA encoding epsilon may be recombinogenic. Mutations within epsilon can affect its function and sequence conservation within epsilon in natural isolates is therefore high. epsilon could provide a practical target for antiviral therapy.
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Affiliation(s)
- A Kramvis
- Department of Medicine, University of the Witwatersrand, Johannesburg, South Africa
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41
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de Haan CA, Vennema H, Rottier PJ. Coronavirus envelope assembly is sensitive to changes in the terminal regions of the viral M protein. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1998; 440:367-75. [PMID: 9782305 DOI: 10.1007/978-1-4615-5331-1_48] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
Recently we demonstrated that the co-expressed coronavirus membrane proteins have the capacity to assemble viral envelopes which are similar to normal virus particles in dimensions and appearance, and which can form independent of a nucleocapsid (Vennema et al., 1996). For the formation of these particles only the M and the E protein are required; the S protein is dispensable but is incorporated when present. As we illustrate here, this virus-like particle assembly system is an ideal tool to study the interactions between the essential assembly partners M and E in molecular detail. Taking a mutagenetic approach we demonstrate that envelope assembly is critically sensitive to changes in the primary structure of both terminal domains of the M protein. The effects were most dramatically observed after mutation of the carboxy-terminal domain where the deletion of just one single amino acid at the extreme terminus abolished particle formation almost completely. But also some subtle mutations in the amino-terminal domain were severely inhibitory to the assembly process. Interestingly, mutant M proteins that were themselves incompetent to support particle formation appeared to inhibit, in a concentration dependent manner, the assembly of particles by wild-type M and E protein.
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Affiliation(s)
- C A de Haan
- Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, The Netherlands
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42
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de Haan CA, Kuo L, Masters PS, Vennema H, Rottier PJ. Coronavirus particle assembly: primary structure requirements of the membrane protein. J Virol 1998; 72:6838-50. [PMID: 9658133 PMCID: PMC109893 DOI: 10.1128/jvi.72.8.6838-6850.1998] [Citation(s) in RCA: 195] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Coronavirus-like particles morphologically similar to normal virions are assembled when genes encoding the viral membrane proteins M and E are coexpressed in eukaryotic cells. Using this envelope assembly assay, we have studied the primary sequence requirements for particle formation of the mouse hepatitis virus (MHV) M protein, the major protein of the coronavirion membrane. Our results show that each of the different domains of the protein is important. Mutations (deletions, insertions, point mutations) in the luminal domain, the transmembrane domains, the amphiphilic domain, or the carboxy-terminal domain had effects on the assembly of M into enveloped particles. Strikingly, the extreme carboxy-terminal residue is crucial. Deletion of this single residue abolished particle assembly almost completely; most substitutions were strongly inhibitory. Site-directed mutations in the carboxy terminus of M were also incorporated into the MHV genome by targeted recombination. The results supported a critical role for this domain of M in viral assembly, although the M carboxy terminus was more tolerant of alteration in the complete virion than in virus-like particles, likely because of the stabilization of virions by additional intermolecular interactions. Interestingly, glycosylation of M appeared not essential for assembly. Mutations in the luminal domain that abolished the normal O glycosylation of the protein or created an N-glycosylated form had no effect. Mutant M proteins unable to form virus-like particles were found to inhibit the budding of assembly-competent M in a concentration-dependent manner. However, assembly-competent M was able to rescue assembly-incompetent M when the latter was present in low amounts. These observations support the existence of interactions between M molecules that are thought to be the driving force in coronavirus envelope assembly.
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Affiliation(s)
- C A de Haan
- Institute of Virology, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, and Institute of Biomembranes, Utrecht University, 3584 CL Utrecht, The Netherlands
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43
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Abstract
Hepatitis B virus small surface protein is synthesized as a transmembrane protein of the rough endoplasmic reticulum (RER) and then buds into the lumen in the form of subviral particles that are secreted. The closely related large surface protein is also targeted to the RER but is retained in a pre-Golgi compartment and cannot be secreted. It has been assumed that the large surface protein remains as a transmembrane RER protein and hence cannot form particles, possibly because of binding to a host factor on the cytosolic face of the RER membranes. We have reexamined this question and found the following results. (i) The retained large surface protein is associated not with RER but, rather, with a more distal compartment. (ii) Electron microscopy reveals intravesicular 20-nm particles, similar to those formed by the small surface protein. (iii) The large surface protein colocalizes with and binds to calnexin, an ER chaperone protein. Therefore, our results indicate that the large surface protein is capable of budding and forming particles, and hence its intracellular retention cannot be attributed to a cytosolic factor. We interpret the data as evidence that the large surface protein is retained by virtue of interacting with calnexin, a component of what is considered the quality control mechanism of the ER.
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Affiliation(s)
- Z Xu
- Department of Pathology, University of California, Veterans Affairs Medical Center, San Francisco, USA
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44
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Marzolo MP, Bull P, González A. Apical sorting of hepatitis B surface antigen (HBsAg) is independent of N-glycosylation and glycosylphosphatidylinositol-anchored protein segregation. Proc Natl Acad Sci U S A 1997; 94:1834-9. [PMID: 9050865 PMCID: PMC20003 DOI: 10.1073/pnas.94.5.1834] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We have used the hepatitis B surface antigen (HBsAg) as a tool to explore mechanisms by which polarized epithelial cells address specific proteins to their apical domain. It recently has been proposed that N-glycans can serve as apical signals recognized by lectin-like sorting receptors in the trans-Golgi network. We found, however, conclusive evidence that the HBsAg follows an apical pathway not mediated by N-glycan signaling. Neither tunicamycin treatment nor replacement of its single glycosylated residue, Asn-146, altered its predominant (>85%) apical secretion from transfected Madin-Darby canine kidney cells (MDCK). Although HBsAg is known to be secreted as a lipoprotein particle, our results suggest that the exocytic machinery involved in its N-glycan-independent pathway overlaps, at least partially, with that of other apically targeted proteins, including the endogenous gp80, as judged by the effects of brefeldin A. We also tested whether its sorting behavior could be ascribed to association with glycosylphosphatidylinositol (GPI)-anchored proteins, which, together with glycosphingolipids, primarily are targeted to the apical domain of MDCK cells. HBsAg was preferentially secreted from the apices of transfected Fisher rat thyroid cells, which, in contrast to MDCK cells, address GPI-proteins and glycosphingolipids to their basal domain. Moreover, complete inhibition of GPI biogenesis by mannosamine treatment did not impair the HBsAg apical secretion, discarding the possibility that HBsAg could be "hitchhiking" with a newly synthesized GPI-protein. Thus, the HBsAg provides a unique model system to search for yet-unknown apical sorting mechanisms that could depend on proteinaceous targeting signals interacting with cognate trans-Golgi network receptors that are at present unidentified.
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Affiliation(s)
- M P Marzolo
- Departamento de Immunologia Clínica y Reumatología, Facultad de Medicina, Pontifica Universidad Católica de Chile, Santiago
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45
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Poisson F, Severac A, Hourioux C, Goudeau A, Roingeard P. Both pre-S1 and S domains of hepatitis B virus envelope proteins interact with the core particle. Virology 1997; 228:115-20. [PMID: 9024817 DOI: 10.1006/viro.1996.8367] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The three envelope proteins of the hepatitis B virus (HBV) are encoded by a single open reading frame in the genome containing three separate in-phase AUG codons. This organization defines three protein domains (pre-S1, pre-S2, S) which form the small (S), middle (M, pre-S2/S), and large (L, pre-S1 /pre-S2/S) proteins. Mature virions are generated by the budding of preformed nucleocapsids through endoplasmic reticulum (ER) membranes containing S and L proteins, whereas the M protein is not necessary. This suggests an important function for the pre-S1 domain. To investigate the protein-protein interactions involved during the maturation process of the HBV virion, we studied in vitro the binding affinity to purified HBV core particles of various synthetic peptides identical to regions of the envelope proteins. Data previously obtained with deletion mutants were confirmed and refined. The 13 C-terminal amino acids of pre-S1 bound efficiently to core particles, whereas other pre-S domains did not. Moreover, the amino acid sequence 56-80 in the cytosolic loop of S bound efficiently to the HBV core. This double interaction between the HBV capside and both S and pre-S1 domains may be required for virion morphogenesis.
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Affiliation(s)
- F Poisson
- Laboratoire de Virologie URA CNRS 1334, Faculté de Médecine de Tours,France
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46
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Guo JT, Pugh JC. Topology of the large envelope protein of duck hepatitis B virus suggests a mechanism for membrane translocation during particle morphogenesis. J Virol 1997; 71:1107-14. [PMID: 8995631 PMCID: PMC191162 DOI: 10.1128/jvi.71.2.1107-1114.1997] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We have investigated the membrane topology of the large envelope protein of duck hepatitis B virus (DHBV) by protease protection and Western blot analysis, using monoclonal antibodies specific for the pre-S and S regions of the DHBV envelope to characterize protease-resistant polypeptides. These studies showed that DHBV L protein exhibits a mixed membrane topology similar to that of human hepatitis B virus L, with approximately half of the L molecules displaying pre-S on the surface of virus particles and the remainder with pre-S sequestered inside the virus envelope. The C-terminal region of DHBV pre-S was susceptible to protease digestion on all DHBV particle L protein, indicating that this region was externally disposed. DHBV L protein pre-S was entirely cytosolic immediately after synthesis. Our data, therefore, suggested that an intermediate form of the DHBV L molecule exists in mature envelope particles in which L is partially translocated or exists in a translocation-ready conformation. Incubation of virus particles at low pH and 37 degrees C triggered conversion of this intermediate into a fully translocated form. We have proposed a model for pre-S translocation based on our results that invokes the presence of an aqueous pore in the virus envelope, most likely created by oligomerization of transmembrane domains in the S region. The model predicts that pre-S is transported through this pore and that a loop structure is formed because the N terminus remains anchored to the inner face of the membrane. This translocation process occurs during particle morphogenesis and may also be a prerequisite to virus uncoating during infection.
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Affiliation(s)
- J T Guo
- Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA
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47
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Abstract
According to the present model for assembly of alphaviruses, e.g. Semliki Forest virus (SFV), the viral genome is first encapsidated into a nucleocapsid (NC) in cytoplasm and this is then used for budding at plasma membrane (PM). The preformed NC is thought to act as a template on which the viral envelope can be organized. In the present work we have characterized two SFV deletion mutants which did not assemble NCs in the cytoplasm but which instead appeared to form NCs at the PM simultaneously with virus budding. The deletions were introduced in a conserved 14 residue long linker peptide that joins the amino-terminal RNA-binding domain with the carboxy-terminal serine-protease domain of the capsid protein. Despite the deletions and the change in morphogenesis, wild-type (wt)-like particles were produced with almost wt efficiency. It is suggested that the NC assembly defect of the mutants is rescued through spike-capsid interactions at PM. The results show that the preassembly of NCs in the cytoplasm is not a prerequisite for alphavirus budding. The apparent similarities of the morphogenesis pathways of wt and mutant SFV with those of type D and type C retroviruses are discussed.
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Affiliation(s)
- K Forsell
- Department of Bioscience at Novum, Huddinge, Sweden
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Suomalainen M, Hultenby K, Garoff H. Targeting of Moloney murine leukemia virus gag precursor to the site of virus budding. J Cell Biol 1996; 135:1841-52. [PMID: 8991095 PMCID: PMC2133957 DOI: 10.1083/jcb.135.6.1841] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Retrovirus Moloney murine leukemia virus (M-MuLV) matures by budding at the cell surface. Central to the budding process is the myristoylated viral core protein precursor Gag which, even in the absence of all other viral components, is capable of associating with the cytoplasmic leaflet of the plasma membrane and assembling into extracellular virus-like particles. In this paper we have used heterologous, Semliki Forest virus-driven, expression of M-MuLV Gag to study the mechanism by which this protein is targeted to the cell surface. In pulse-chase experiments, BFA, monensin, and 20 degrees C block did not affect incorporation of Gag into extracellular particles thereby indicating that the secretory pathway is not involved in targeting of Gag to the cell surface. Subcellular fractionation studies demonstrated that newly synthesized Gag became rapidly and efficiently associated with membranes which had a density similar to that of plasma membrane-derived vesicles. Protease-protection studies confirmed that the Gag-containing membranes were of plasma membrane origin, since in crude cell homogenates, the bulk of newly synthesized Gag was protease-resistant as expected of a protein that binds to the cytoplasmic leaflet of the plasma membrane. Taken together these data indicate that targeting of M-MuLV Gag to the cell surface proceeds via direct insertion of the protein to the cytoplasmic side of the plasma membrane. Furthermore, since the membrane insertion reaction is highly efficient and specific, this suggests that the reaction is dependent on as-yet-unidentified cellular factors.
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Tavis JE, Ganem D. Evidence for activation of the hepatitis B virus polymerase by binding of its RNA template. J Virol 1996; 70:5741-50. [PMID: 8709189 PMCID: PMC190587 DOI: 10.1128/jvi.70.9.5741-5750.1996] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The hepatitis B viruses replicate by reverse transcription of an RNA pregenome by using a virally encoded polymerase. A key early step in replication is binding of the polymerase to an RNA stem-loop (epsilon) of the pregenome; epsilon is both the RNA encapsidation signal and the origin of reverse transcription. Here we provide evidence that this interaction is also key to the development of enzymatic activity during biosynthesis of the polymerase. Duck hepatitis B virus polymerase expressed in Saccharomyces cerevisiae can synthesize DNA from epsilon-containing RNAs and can also end label other small RNAs. Expression of functional polymerase in S. cerevisiae requires interaction between the polymerase and epsilon during or shortly after translation for it to develop any enzymatic activity; if epsilon is absent during expression, the polymerase is inactive on RNAs both with and without epsilon. Functional duck polymerase can also be produced by in vitro translation, and synthesis of the polymerase in the presence of epsilon induces resistance in the polymerase to proteolysis by papain, trypsin, and bromelain. Induction of the resistance is specific for epsilon sequences that can support RNA encapsidation and initiation of DNA synthesis. Induction of the resistance precedes initiation of DNA synthesis and is reversible by degradation of epsilon. These two sets of data (i) support a model in which binding of epsilon to the polymerase induces a structural alteration of the polymerase prior to the development of enzymatic activity and (ii) suggest that this alteration may be required for the polymerase to mature to an active form.
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Affiliation(s)
- J E Tavis
- Department of Molecular Microbiology and Immunology, St. Louis University School of Medicine, Missouri 63104, USA.
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Wounderlich G, Bruss V. Characterization of early hepatitis B virus surface protein oligomers. Arch Virol 1996; 141:1191-205. [PMID: 8774681 DOI: 10.1007/bf01718824] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The small surface protein (S) of the hepatitis B virus (HBV) is synthesized as unglycosylated p24 and N-glycosylated gp27 and forms disulfide linked dimers. Former models proposed that these complexes consist preferentially of p24-gp27 heterodimers. Furthermore, cell free in vitro experiments suggested that p24 has a transmembrane topology different from gp27. We tested these models by expressing the HBV surface proteins in transfected cell cultures and characterizing early maturation products after short pulse labelings. Two dimensional unreduced-reduced polyacrylamide gel electrophoresis demonstrated that p24 and gp27 dimerized without preference for a specific pairing. Protease protection experiments showed that both, p24 and gp27, had identical transmembrane topologies in cell culture. The middle sized (M) and large HBV surface proteins formed mixed dimers with the S protein. Mutant M and S protein in which all 10 cysteine residues in the ectodomain and transmembrane regions were replaced by serine residues formed no intermolecular S-S bridges but were secreted like wild type M and S protein.
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Affiliation(s)
- G Wounderlich
- Department of Medical Microbiology, University of Göttingen, Federal Republic of Germany
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